1. Field of the Invention
This invention relates to the field of fluid delivery and more specifically to apparatus and method for switching reactive and inert fluid with high speed and performance.
2. Description of Prior Art
In the fabrication of semiconductor and similar devices, substrates are being processed under conditions of controlled ambient, which is accomplished within enclosed spaces, or chambers, wherein fluids are delivered and exhausted. Shutoff valves are commonly used to route the flow of fluids such as gasses and liquids within fluid delivery manifolds. In particular, diaphragm-based high purity and ultrahigh purity valves are commonly used to command the flow of inert and reactive gas within high purity manifolds that are kept under tight standards of low-contamination levels.
Typically, a dome-shaped preformed metallic diaphragm is implemented to create an all-metallic valve chamber over a valve seat. The valve seat typically implements a polymeric seal and is commonly located at the center of the valve chamber, across from the diaphragm. The diaphragm is clamped at the perimeter and is normally held at the unstressed dome shape. When the diaphragm is not stressed, a fluid path is linked, through the valve seat, with at least another fluid path that communicatively runs into the valve chamber. Accordingly, the shutoff valve is “OPEN”. To shut the valve off, the diaphragm is deflected towards the valve seat by a mechanical plunger to enclose the fluid path that runs through the valve seat. A leak-free seal is accomplished with appropriately selected valve seat material and matching sealing pressure applied by the plunger over the diaphragm. When the stress is removed from the diaphragm, the diaphragm flexes back to the dome shape to clear the fluid path within the valve. The art of high purity diaphragm valves includes a selection of different valve seat and diaphragm designs that are proven useful for high-purity switching of fluids. For example, U.S. Pat. No. 5,131,627 articulates several useful methods to accomplish a reliable valve at high standards of purity.
In the art of fluid control, the need exists to construct fail-safe valves that are normally closed when the valve is not energized. In particular, fail-safe valves are mandatory within manifolds that are built to deliver hazardous or otherwise reactive chemicals and gasses. Accordingly, normally closed diaphragm valves are adapted with a spring-loaded plunger called the valve-stem. For example, the disclosure in U.S. Pat. No. 5,131,627 accommodates the valve stem and an energized spring within the valve bonnet. Fail-safe diaphragm valves are actuated to open the fluid path when the spring-loaded valve stem is pulled away from the diaphragm. When these fail-safe valves are not actuated, they return to their “normally-closed” position.
Automatic actuation of fail-safe normally-closed (FSNC) valves is accomplished with a machine commanded actuator. The art of machine commanded actuators includes pneumatic, electromechanical, piezoelectric and electro-thermal stem-actuation. Pneumatic-actuation has been the most widely accepted method for machine commanded valve actuation due to its superior reliability, safety and low cost. For example, a piston type pneumatic actuator of a specific useful design is provided in U.S. Pat. No. 5,131,627. Likewise, many other embodiments are suggested within the prior art commonly with one or multiple pistons that are arranged with a sliding seal within a matching cylinder and are actuated when compressed fluid, typically air, is communicated into the cylinder. The pressurized fluid applies force on the sliding pistons to propel the motion of the pistons within the cylinder. Typically, the valve stem is rigidly attached to the pistons. The fluid is introduced to propel the pistons and the attached valve stem to move away from the diaphragm. Commonly, metallic diaphragms are pre-formed to a deformation-free state wherein a gap exists between the mounted diaphragm and the valve seat corresponding to an open valve. When the valve stem is removed from the diaphragm, the diaphragm flexes, by its own elasticity, back to the stress-free form. When the fluid is released from the pneumatic actuator, the valve stem is returned by the force of the energized spring to the normally-closed position. The rigidly attached pistons are also returned to the de-energized position.
Many different combinations of FSNC diaphragm valves and pneumatic actuators are known in the art. Within the prior art, well-optimized valve designs were adapted to provide minimized leak rate when the valve is closed and adequate response when the valve is actuated with standard pressurized air in the typical range from 40-100 psig. A well-known tradeoff exists between the need for adequately sealed valve and a quickly closing valve, promoted by a strongly loaded spring, and the need for fast valve opening response. Strongly loaded springs are also notorious to promote fast diaphragm and seat wear as well as particle generation from the impact of the diaphragm over the valve seat.
Commonly used diaphragms are light-weight (˜0.2 gm) and are capable of deflection with sub-millisecond response with the impact of relatively small forces. In contrast, pneumatic actuators represent a substantial mass (˜10 grams) and additional friction (between the pistons and the cylinder) that are burdens for high-speed actuation. Nevertheless, these mass and friction impairments can be overcome with a combination of a strongly energized spring (to aid in fast valve closing action) and high-pressure actuation (to overcome the strongly energized spring and provide fast piston acceleration). However, the necessary tradeoff between diaphragm cycle lifetime and speed has commonly set a limitation on pneumatically actuated FSNC valves within the range from 25-80 msec and typically within the range from 40-50 msec. Within these performance limitations, pneumatically actuated FSNC valves have been proven to be useful and adequate for most applications with cycle lifetimes within the range of 1,000,000-10,000,000 cycles, which is proven to be cost effective and appropriate.
Alternatively, diaphragm actuation was implemented with electromechanical (electrically driven, typically solenoid driven) actuators. In this case a valve stem is settled into the normally closed position with a preloaded spring. The stem can be pulled away from the seat by means of electromagnetic energy. For example U.S. Pat. No. 6,394,415 discloses valve apparatus that is capable of 3-5 msec open-close valve response time. While this technology represents a speed improvement over conventional FSNC pneumatic valves it is currently limited to significantly small conductance (Cv=0.1) and low temperature operation.
Diaphragm actuation was also implemented with piezoelectric actuators. These actuators are relatively fast with response time approaching the 2 msec range. While these actuators show promise for high purity applications, they are not compatible, in their ultrahigh-purity version, with FSNC needs. In addition, conductance is relatively limited at the Cv<0.1 range.
The prior art implemented high purity and ultrahigh purity diaphragm valves with the metallic diaphragm serving both as the seat sealing member and the ambient sealing member. This design advantageously minimizes sources of contamination and fluid entrapment as described in the prior art. However, diaphragms were occasionally subjected to catastrophic failure such as rupturing and cracking with subsequent potentially hazardous leakage of dangerous and/or environmentally incompatible fluid into the ambient. In particular, reactive or toxic gasses were occasionally released into the ambient by failing diaphragm valve. This impairment resulted in significant safety and environmental concern and subsequent costly measures to minimize the hazards such as de-rated cycle lifetimes, ventilated and tightly monitored cabinets and multiple containment.
The art of ultrahigh purity diaphragm valves has been a late follower of a well developed diaphragm valve technology that is known and well-documented for over a century with widespread applications spanning from agriculture, analytical instrumentation, plumbing, automotive, aviation, hydraulics and fluid level control to name only a few. Diaphragm actuation with pressurizing fluid has been practiced for many of these applications that do not mandate FSNC valves. In this case diaphragm chambers were formed both at the flow side and the control side (the other side of the diaphragm). The diaphragm was flexed into sealing position by supplying pressurized fluid into the diaphragm control chamber. Valve response time directly corresponds and faithfully follows the timing of fluid pressurization (valve set to be shut-off) and de-pressurization (valve is relieved back to the normally open state). Many useful devices and manifolds were implemented with fluid controlled diaphragm valves such as pressure regulators and self-compensating shut-off valves. Fluid controlled diaphragm valves were utilized for many applications that do not mandate FSNC design. For example, fast gas introduction into chromatography analytical instruments. For example, U.S. Pat. No. 4,353,243 discloses an embodiment for a direct fluid actuated diaphragm valve, configured and suitable for sample introduction within gas chromatography applications. Embodiments within this patent and other patents have successfully implemented polymer or elastomer based diaphragms for adequately performing valve seal with a simple seat design including only a flat surface and a port. U.S. Pat. No. 4,353,243 also suggested the possible utilization of a metallic diaphragms wherein an adequate seal might be obtained by means of a polymer coating over the internal area of the diaphragm.
Conventional ultrahigh-purity diaphragm and valve seat designs are mostly suitable for mechanical actuation, localized at the center of the diaphragm, which was practiced in the prior art. In contrast, fluid actuation, by virtue of applying a uniformly distributed force has the tendency to spread the inverted part of the diaphragm across an area that is substantially larger than the common valve seat. Accordingly, conventional fluid-controlled diaphragm valves were designed for large area contact between the diaphragm and a flat seat. However, this design is not compatible with high purity valves wherein large area contacts are disadvantageous. Additionally, an area based leak-tight sealing is not practically possible with metallic diaphragms.
Diaphragm valves are inherently limited in conductance. Valve conductance is restricted by the limited range of diaphragm flexing. There is a recognized tradeoff between diaphragm cycle lifetime (the number of cycles until failure) and the increase in diaphragm flexing (to increase conductance). Accordingly, standard size high-purity diaphragm valves were limited in conductance to the Cv range from 0.05-0.50. Where Cv represents the flow through a valve under a standard pressure gradient of 1 psi. For example, a Cv range from 0.1-0.5 represents a valve path opening in the approximate range from 2-16 mm2 of area. It is well known in the art that diaphragm cycle lifetime is adversely impacted by increased range of diaphragm flexing making higher conductance valve, generally less reliable.
Modified diaphragms were invented for increased conductance while minimizing the tradeoff of cycle lifetime. For example U.S. Pat. No. 5,201,492 discloses a high purity valve embodiment wherein the diaphragm comprises several annular surfaces that are stepped upward from a plane in which the diaphragm perimeter is secured to the valve body. Accordingly, larger and more consistent conductance was materialized. In the art of gas pressure sensors, corrugated and rippled flexible-metallic-diaphragms were used to improve the performance and reliability of pressure sensing devices, for example, the embodiments disclosed in U.S. Pat. No. 4,809,589.
Diaphragm valves are typically limited to operate within the temperature range that is compatible with the valve seat material. For example, typical ultrahigh-purity diaphragm valves were successfully implemented with Kel-F (PCTFE) seat material. Kel-F has been implemented with superior reliability in the temperature range up to 65° C. while maintaining a resilient and leak-tight seal. Higher operation temperature, typically up to 125° C., was attainable with the aid of polyimide polymer seat material such as Vespel®. Adequate leak integrity over much harder Vespel seats typically requires to strengthen the preloaded spring. To match the opening speed to the closing speed, high temperature valves are typically actuated at higher air pressure in the range from 60-100 psig. Accordingly, higher temperature valves can be actuated faster than low temperature valves. However, the resulted higher stem impact on the diaphragm adversely shortens the cycle lifetime of diaphragms with adverse impact on the reliability and cleanliness. In addition, the diaphragm slamming over a much harder seat material, such as Vespel inevitably accelerates diaphragm and seat wear and particle formation. Vespel is considerably more brittle than other lower temperature seat materials such as Kel-F. While Vespel based higher temperature valves have been offered in the commercial market for several years they are still immature and inadequate for most applications.
High purity and ultra-high-purity (UHP) valves were successfully installed for reliable and cost effective functionality of many different processing equipment such as chemical vapor deposition (CVD), physical vapor deposition (PVD) and etching. In these applications, valves are typically cycled once during process. Accordingly, reliable and contamination-free cycle lifetime in the range from 1,000,000-10,000,000, that was tested and specified for these valves, enabled the processing of many substrates with valve actual lifetime exceeding 5 years.
In recent years, the art of semiconductor processing and similar arts have created a commercial market for multiple valve manifolds. Within multiple valve manifolds, several valves are connected into a functioning control device wherein simultaneous and/or coordinated actuation of several valves with precision is essential. For example, the common-functionality of routing a fluid entering from one common port into either one of two “non-common” ports requires the synchronized actuation of two separate valves. In the art of multiple valve manifolds, valve state uncertainty, during the period of valve response time is undesired. Within larger manifolds of three valves and more gas counter-flow may result if the valves are operated out of synchronization. Particular applications of reactive gas mixing manifolds cannot tolerate counter-flow and require sophisticated and functionality impaired valve delay actuation to avoid source gas and manifold contamination. Accordingly, conventional FSNC valves with their associated 40-50 msec response time are inadequate for many of these forefront applications in the semiconductor, display and pharmaceutical manufacturing industries, to name a few.
In was further recognized, in recent years that the speed and the synchrony of valves can be improved by integrating a pilot valve together with a FSNC valve wherein the delay and inconsistency associated with pneumatic hoses is avoided. For example U.S. Pat. No. 5,850,853 describes an assembly of a conventional FSNC pneumatic valve with a standard solenoid valve wherein the air pressure is fed into the solenoid valve and the valve is actuated by controlling electrical current to the pilot valve. Unfortunately, integrated pneumatic-pilot valves do not represent a substantially improved prior art in terms of speed and cycle lifetime.
In recent years, atomic layer deposition (ALD), a variant of CVD has emerged as the future work-horse deposition method for critical thin film applications. ALD is a cyclic process carried out by dividing conventional chemical vapor deposition (CVD) process into an iterated sequence of self-terminating process steps. An ALD cycle contains several (at least two) chemical dose steps in which reactive chemicals are separately delivered into the process chamber. Each dose step is typically followed by an inert gas purge step that eliminates the reactive chemicals from the process space prior to introducing the next precursor.
ALD films of practical thickness typically require between several tens to several thousands of valve cycles per layer. In contrast, most other processes such as CVD, PVD, etching etc. are practiced with only one valve cycle per layer. Accordingly, much higher standards for valve cycle lifetime are required for cost effective ALD performance. Additionally, cost-effective ALD mandates typical valve cycle times on the order of 10-100 msec and acceptable valve response time must be limited to 5 msec, or less. Moreover, efficient switching delivery of low-volatility ALD precursors with limited volatility imposes higher specifications for valve conductance and temperature rating than the specifications of currently available high purity valves.
For example, an ALD process with 200 cycles wears out the valves at least 200 times faster than a CVD process, therefore reducing practical valve lifetime from 5 years into a mere 10 days for a valve with cycle lifetime of 1,000,000 cycles. It was also discovered, by the inventor of this invention and others, that under high throughput ALD conditions wherein valves are cycled within 10-150 msec, off-the-shelf valves are typically wearing about 10 times faster than their specified cycle lifetime. This undesired phenomenon was found empirically to be the general trend independent of valve manufacturer or model. As a result, even top performing commercialized valves are expected to last only 5-30 days under high-productivity-ALD production environment.
Independently, the 25-80 msec response of standard UHP valves introduces an uncontrolled timing uncertainty for valve opening and shutting on the order of 10-40 msec. This range of uncontrolled time mismatch is comparable and longer than typical flow resident time during ALD purge which for high throughput ALD is preferably set below 5 msec. With chemical dose step being slotted into a 10-100 msec range, a possible 10-40 overlap between ALD chemical dose steps and ALD purge steps is devastating. Even worse, during actuation the conductance of the valves is poorly defined and generally inconsistent. As ALD manifolds are in particular designed for fast response, they are very sensitive to counter-flow from non-synchronous actuation of valves. Therefore, it is necessary to maintain valve actuation times to be substantially shorter than valve cycle time (the time it takes to open, keep open and close the valve) and in general, as short as possible.
Ideally, ALD should be practiced with injection type valves notated in the art as “pulsed valves”. However, prior art injection valves are not compatible with high purity standards. Likewise, prior art high purity valve technology is not suitable for injection valve applications.
To summarize, the need for improved performance of multiple-valve-manifolds created a necessity for FSNC valves with substantially faster response and time precision. These valves must achieve more than an order of magnitude improved speed while maintaining and preferably improving valve-cycle lifetime. In particular, a substantially improved valve response and cycle lifetime are necessary to support the transition of ALD into mass-production. There is also a need to increase the conductance and the temperature rating of all-metal high purity valves while maintaining their reliability, cleanliness and long cycle lifetime. Finally, there is also a need for high purity FSNC injection valves with the specifications of speed and reliability stated herein.